Enzymatic process for production of modified hop products

ABSTRACT

The present invention relates to a process for producing a beer bittering agent via enzyme catalyzed bioconversion of hop-derived isoalpha acids to dihydro-(rho)-isoalpha acids.

REFERENCE TO SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM

The Sequence Listing concurrently submitted herewith under 37 CFR §1.821 in a computer readable form (CRF) via EFS-Web as file nameKALSEC_75_US_SEQ_LISTING.txt is herein incorporated by reference. Theelectronic copy of the Sequence Listing was created on 25 Sep. 2019,with a file size of 259 kilobytes.

FIELD OF THE INVENTION

The present invention relates to a process for producing a beerbittering agent via enzyme catalyzed bioconversion of hop-derivedisoalpha acids to dihydro-(rho)-isoalpha acids. Dihydro-(rho)-isoalphaacids have superior characteristics which improve utility as a beverageadditive. Consumers may prefer dihydro-(rho)-isoalpha acids produced viathis process, which does not require the use of harsh chemical reagentsand which utilizes enzymes which may be naturally occurring.

BACKGROUND OF THE INVENTION

Traditional methods of bittering beer use whole fresh hops, whole driedhops, or hop pellets added during the kettle boil. Hop extracts made byextracting hops with supercritical carbon dioxide, or isomerized hoppellets, made by heating hops in the presence of a catalyst are morerecent bittering innovations that have also been adopted by brewers. Hoppellets can also be added later in the brewing process and in the caseof dry hopping, hops are added to the finished beer prior to filtration.These methods suffer from a poor utilization of the bittering compoundspresent in the hops, which impacts the cost unfavorably. Beer or othermalt beverages produced in this manner are unstable to light and must bepackaged in dark brown bottles or cans or placed to avoid the lightinduced formation of 3-methyl-2-butene-1-thiol (3-MBT) which gives apronounced light-struck or skunky aroma. Placing bottles in cardboardboxes or completely wrapping them in light-proof or light-filteringpaper, foil, or plastic coverings is another expensive method ofprotecting these beverages from light-struck flavor and aroma.

Bitterness in traditionally brewed beer is primarily derived fromisoalpha acids. These compounds are formed during the brewing process bythe isomerization of the humulones, which are naturally occurringcompounds in the lupulin glands of the hop plant. A consequence of thisis, given the natural instability of the isoalpha acids towardsphotochemical reactions in beer, a beverage prone to the formation oflight-struck or skunky flavor and aroma.

Fully light stable beers or other malt beverages can be prepared usingso-called advanced or modified hop acids. Beers made using thesebittering agents can be packaged in non-colored flint glass bottleswithout fear of forming skunky aromas. Dihydro-(rho)-isoalpha acids arereduction products of isoalpha acids which are light stable. To date,these compounds have not been found in nature. Traditionally, theportion of the isoalpha acids which is responsible for thephotochemistry has been altered by reduction of a carbonyl group usingsodium borohydride.

Sodium borohydride is an inorganic compound that can be utilized for thereduction of ketones. It is extremely hazardous in case of skin contact,eye contact, inhalation, or ingestion, with an oral LD50 of 160 mg/kg(rat). Sodium borohydride is also flammable, corrosive, and extremelyreactive with oxidizing agents, acids, alkalis, and moisture (SodiumBorohydride; MSDS No. S9125; Sigma-Aldrich Co.: Saint Louis, Mo. Nov. 1,2015.

Consumers are increasingly expressing a preference for natural materialsover synthetic or semi-synthetic ones. Thus, a need exists not only toprovide compositions employing natural materials as bittering agents forbeer and other beverages, but also processes for more natural productionof said materials.

Biocatalytic production is an emerging technology which provides highlyselective, safe, clean, and scalable production of high value compounds.Biocatalytic production relies on naturally occurring enzymes to replacechemical catalysts.

Enzymes are naturally occurring proteins capable of catalyzing specificchemical reactions. Enzymes exist in nature that are currently capableof replacing chemical catalysts in the production of modified hopbittering compounds (Robinson, P. K., Enzymes: principles andbiotechnological applications. Essays Biochem 2015, 59, 1-41.).

Humulone is a natural secondary metabolite that would be exposed tofungi and bacteria cohabitating with the plant, Humulus lupulus. It ispossible that soil- and plant-dwelling fungi and bacteria possessenzymes capable of modifying humulone for detoxification or scavengingpurposes. Additionally, organisms may have evolved enzymes to modifyhumulone-like molecules, but because of promiscuous activity, theseenzymes possess activity against the compounds of interest, isoalphaacids (Hult, K.; Berglund, P., Enzyme promiscuity: mechanism andapplications. Trends Biotechnol. 2007, 25 (5), 231-238; Nobeli, I.;Favia, A. D.; Thornton, J. M., Protein promiscuity and its implicationsfor biotechnology. Nat. Biotechnol. 2009, 27 (2), 157-167.).

Enzymes which catalyze oxidation/reduction reactions, that is transferof hydrogen and oxygen atoms or electrons from one substance to another,are broadly classified as oxidoreductases. More specifically, enzymesthat reduce ketone groups to hydroxyl groups are known as ketoreductasesor carbonyl reductases and depend on the supplementation of an exogenoussource of reducing equivalents (e.g. the cofactors NADH, NADPH).Consistent with the existing naming of the enzymes characterized herein,the enzymes will be referred to as a “ketoreductases”.

The cost of expensive cofactors (NADH, NADPH) can be reduced byincluding additional enzymes and substrates for cofactor recycling, forexample glucose dehydrogenase and glucose, or by utilizing aketoreductase that is also capable of oxidizing a low-cost and naturalfeedstock, such as ethanol.

Abundant precedence exists for the utility of enzymes in brewing andtheir favorable influence on the final character of beer (Pozen, M.,Enzymes in Brewing. Ind. Eng. Chem, 1934, 26 (11), 1127-1133.). Thepresence of yeast enzymes in the natural fermentation of beer is knownto produce compounds that affect the flavor and aroma of the finalbeverage (Praet, T.; Opstaele, F.; Jaskula-Goiris, B.; Aerts, G.; DeCooman, L., Biotransformations of hop-derived aroma compounds bySaccharomyces cerevisiae upon fermentation. Cerevisia, 2012, 36,125-132.). Exogenously added enzymes provide a variety of improvementsto the brewing process, such as reduced viscosity, increased fermentablesugars, chill-proofing and clarification (Wallerstein, L. (1947)Bentonite and Proteolytic Enzyme Treatment of Beer, U.S. Pat. No.2,433,411.; Ghionno, L.; Marconi, O.; Sileoni, V.; De Francesco, G.;Perretti, G., Brewing with prolyl endopeptidase from Aspergillus niger:the impact of enzymatic treatment on gluten levels, quality attributes,and sensory profile. Int. J. Food Sci. Technol, 2017, 52 (6),1367-1374.). Additionally, hop extracts have been specificallypretreated with enzymes for modifying hop-derived aroma compounds (Gros,J.; Tran, T. T. H.; Collin, S., Enzymatic release of odourantpolyfunctional thiols from cysteine conjugates in hop. J. Inst. Brew.2013, 119 (4), 221-227.).

Prior to the present invention, however, enzymes capable of catalyzingthe reduction of isoalpha acids to dihydro-(rho)-isoalpha acids have notbeen observed in nature, and thus have not been described in theliterature. The process disclosed herein represents a novel enzymaticreaction.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a process forenzymatic production of dihydro-(rho)-isoalpha acids, a modified versionof natural bittering agents derived from the hop plant. The presentprocess is designed to replace current production processes whichutilize the chemical reagent, sodium borohydride.

SUMMARY OF THE INVENTION

The present invention relates to a process that can be scaled up toindustrial levels for bioconversion of iso-alpha acids intodihydro-(rho)-isoalpha acids, which can then be used as a naturallyderived and light stable bittering agent in beverages.

One aspect of the present invention is a process for the high-yieldbioconversion of iso-alpha acids into dihydro-(rho)-isoalpha acidsutilizing a ketoreductase enzyme or a microorganism expressing a genethat encodes said ketoreductase.

A further aspect of the invention relates to such a process forproduction of dihydro-(rho)-isoalpha acids, wherein the process iscarried out in an aqueous system with mild temperature and pHconditions, making it an environmentally benign manufacturing process.

In an embodiment of the invention, bioconversion of isoalpha acids todihydro-(rho)-isoalpha acids comprises the addition of purifiedketoreductase enzyme and NADPH or NADP to a mixture of isoalpha acidsfollowed by incubation until the desired yield is obtained.

In another embodiment of the invention, bioconversion of isoalpha acidsto dihydro-(rho)-isoalpha acids comprises the addition of purifiedketoreductase enzyme and NADPH or NADP to a mixture of isoalpha acids inthe presence of isopropanol for cofactor recycling, followed byincubation until the desired yield is obtained.

In a further embodiment of the invention, the concentration of isoalphaacids, i.e. the substrate, is maximized to increase the volumetricproductivity of the bioconversion.

In a further embodiment of the invention, the concentration of thecofactor NADPH or NADP in the mixture is minimized to improve theeconomics of the bioconversion.

In an embodiment of the invention, bioconversion of isoalpha acids todihydro-(rho)-isoalpha acids comprises the addition of purifiedketoreductase enzyme and NADPH or NADP to a mixture of isoalpha acids inthe presence of another enzyme (such as glucose dehydrogenase) forcofactor recycling, followed by incubation until the desired yield isobtained.

In another embodiment of the invention, bioconversion of isoalpha acidsto dihydro-(rho)-isoalpha acids comprises the addition of a whole cellbiocatalyst to a mixture of isoalpha acids followed by incubation untilthe desired yield is obtained, wherein the whole cell biocatalyst is animmobilized microorganism expressing the gene which encodes aketoreductase.

In another embodiment of the invention, bioconversion of isoalpha acidsto dihydro-(rho)-isoalpha acids comprises the feeding of isoalpha acidsto a growing microorganism expressing the gene which encodes aketoreductase.

In another embodiment of the invention, bioconversion of alpha acids todihydro-(rho)-isoalpha acids comprises the addition of thermostableketoreductase enzyme to an extract of alpha acids wherein heat isapplied, and the mixture is incubated until the desired yield ofdihydro-(rho)-isoalpha acids is achieved.

In another embodiment of the invention, the ketoreductase employed inthe process according to the present invention displays a preference forreducing the carbonyl group in the side chain at C(4) of the isoalphaacids, converting the light-sensitive acyloin group to a secondaryalcohol, and producing a light-stable isoalpha acid derivative (FIG. 1).

In another embodiment of the invention, the ketoreductase employed inthe process according to the present invention advantageously displaysminimal or no preference for catalyzing reduction of any one particularmember of the six major isoalpha acids: cis-isohumulone,trans-isohumulone, cis-isocohumulone, trans-isocohumulone,cis-isoadhumulone, and trans-isoadhumulone.

In another embodiment of the invention, the ketoreductase employed inthe process according to the present invention specifically reducescis-isohumulone, cis-isocohumulone, and cis-isoadhumulone.

In another embodiment of the invention, the ketoreductase employed inthe process according to the present invention specifically reducestrans-isohumulone, trans-isocohumulone, and trans-isoadhumulone.

In another embodiment of the invention, a mixture of 2 or moreketoreductase enzymes displaying the above substrate specificity isemployed in the process according to the present invention to reduce amixture of cis- and trans-isoalpha acids, to their respectivedihydroisoalpha acids.

In another embodiment of the invention, a mixture of 2 or moreketoreductase enzymes displaying substrate specificity can be added to areaction mixture to produce a unique mixture of dihydroisoalpha acidsthat is distinct from that produced by chemical reducing agents, such assodium borohydride.

In a further embodiment, the present invention relates to a process asdefined above, wherein the commercially available ketoreductase isselected from KRED-P1-B05, KRED-P2-B02, KRED-P2-C02, KRED-P2-C11,KRED-P2-D11, KRED-P2-G03, KRED-P2-G09, KRED-101, KRED-119, KRED-130,KRED-NADH-110, KRED-430, KRED-431, KRED-432, KRED-433, KRED-434,KRED-435, and KRED-436.

A further embodiment of the invention relates to a ketoreductase enzymewhich comprises the amino acid sequence of SEQ ID NO: 4, SEQ ID NO: 6,SEQ ID NO: 80, SEQ ID NO: 104, SEQ ID NO: 100, SEQ ID NO: 136, SEQ IDNO: 116, SEQ ID NO: 132, SEQ ID NO: 162, SEQ ID NO: 150, SEQ ID NO: 152,SEQ ID NO: 144, SEQ ID NO: 146 or SEQ ID NO: 158.

In a further embodiment, the present invention relates to a process asdefined above, wherein the ketoreductase enzyme or microorganismexpressing a gene which encodes the ketoreductase enzyme can optionallyhave one or more differences at amino acid residues as compared to theketoreductase enzyme which comprises the amino acid sequence of SEQ IDNO: 4, SEQ ID NO: 6, SEQ ID NO: 80, SEQ ID NO: 104, SEQ ID NO: 100, SEQID NO: 136, SEQ ID NO: 116, SEQ ID NO: 132, SEQ ID NO: 162, SEQ ID NO:150, SEQ ID NO: 152, SEQ ID NO: 144, SEQ ID NO: 146 or SEQ ID NO: 158.

In a further embodiment, the present invention relates to a process asdefined above, wherein the ketoreductase is 99, 95, 90, 85, 80, 75 or 70percent homologous to the ketoreductase enzyme which comprises the aminoacid sequence of SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 80, SEQ ID NO:104, SEQ ID NO: 100, SEQ ID NO: 136, SEQ ID NO: 116, SEQ ID NO: 132, SEQID NO: 162, SEQ ID NO: 150, SEQ ID NO: 152, SEQ ID NO: 144, SEQ ID NO:146 or SEQ ID NO: 158.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the enzyme catalyzed reduction of a representative epimerof isoalpha acids.

FIG. 2 shows a UPLC chromatogram for Codexis KRED-P1-B05 (SEQ ID NO: 4)incubated with Isoalpha Acids (acidic solution) for 48 hr at 30° C.

FIG. 3 shows an HPLC chromatogram and peak quantitation for CodexisKRED-P1-B05 (SEQ ID NO: 4) incubated with Isoalpha Acids (acidicsolution) for 48 hr at 30° C.

FIG. 4 shows UPLC chromatogram for Codexis KRED-433 incubated withIsoalpha Acids for 24 hr at 30° C.

FIG. 5 shows improved KRED Activity of SEQ ID NO: 80, 104, 100, 136,116, 132, 162, 150, 152, 144, 146 and 158 at High Substrate and low NADPConcentration.

DETAILED DESCRIPTION OF THE INVENTION

In this invention, a ketoreductase enzyme replaces the function ofsodium borohydride and allows a more natural production method for thebeverage additive, dihydro-(rho)-isoalpha acids. The enzyme may be anyketoreductase specifically reducing a ketone group to a hydroxy group ofany or all isomers of isoalpha acid (co-, n- ad-, and cis/trans-). Theenzyme may be derived from, but not limited to, bacteria, fungi, orplants. The enzyme may be cofactor dependent (NADH or NADPH) orindependent.

Herein, “isoalpha acids”, “hop isoalpha acids”, and “hop-derivedisoalpha acids” may be used interchangeably.

Isoalpha acid solution is subjected to enzymatic treatment using apurified enzyme or a mixture containing an enzyme and optionallyadditional enzymes for cofactor recycling. The amount of enzyme dependson the incubation parameters including duration, temperature, amount andconcentration of substrate.

Alternatively, an isoalpha acid solution is subjected to enzymatictreatment using a mixture containing a microorganism expressing saidenzyme. The invention furthermore provides a process for reducingisoalpha acids according to the invention, which comprises cultivating aketoreductase-producing microorganism, if appropriate inducing theexpression of the ketoreductase. Intact cells can be harvested and addeddirectly to a reaction, in place of isolated enzyme, for the reductionof isoalpha acids as described above. Furthermore, the harvested cellscan be immobilized prior to addition to a reduction reaction. Themicroorganism can be cultivated and fermented by known methods. Themicroorganism can be bacteria or fungi.

A mixture of cis- and trans-isoalpha acids may be incubated with asingle ketoreductase displaying the capacity to reduce both isomers.Alternatively, a mixture of cis- and trans-isoalpha acids may beincubated with 2 or more ketoreductases showing varying specificitywhere the resulting product is a mixture of cis- andtrans-dihydroisoalpha acids.

Alternatively, a solution containing only cis-isoalpha acids may beincubated with a ketoreductase specific for the cis-isomer, and theresulting product is a solution of cis-dihydroisoalpha acids. A solutionof only cis-dihydroisoalpha acids may display advantageous bitternessand/or thermal stability properties.

Alternatively, a solution containing only trans-isoalpha acids may beincubated with a ketoreductase specific for the trans-isomer, and theresulting product is a solution of trans-dihydroisoalpha acids. Asolution of only trans-dihydroisoalpha acids may display advantageousbitterness properties.

Customized blends of trans- and cis-isoalphacids may be incubated with 1or more ketoreductases displaying variable substrate specificity, toproduce unique blends of dihydroisoalpha acids otherwise unattainable.

An isoalpha acid mixture may be subjected to an enzymatic reaction usinga ketoreductase enzyme in addition to enzymes for catalyzing additionaldesired modifications, such as but not limited to, dehydrogenases,isomerases, hydratases and lyases. Enzymes of varying activity may becombined in a one pot reaction or added sequentially.

A suitable solvent to use in the enzyme incubation includes water andmixtures of water with another solvent compatible with the enzyme, suchas ethanol or isopropanol. Enzymatic activity benefits from buffering ofaqueous solutions. Buffering agents include, but are not limited to:tris(hydroxymethyl)aminomethane (aka. Tris),4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (aka. HEPES), sodiumphosphate, and potassium phosphate.

The enzyme and isoalpha acids are incubated within a suitable pH range,for example pH 6 to 10, and temperature range, for example 10 to 90° C.,and held at this temperature for a sufficient time to convert isoalphaacids to the desired dihydro-(rho)-isoalpha acids yield. Continuousstirring will ensure a constant temperature and exposure of substrate toenzyme. The reaction duration, typically 24 to 48 hours, will depend onthe amount and concentration of the enzyme and substrate, solventpresent, and temperature chosen.

Enzyme may be free hi solution, immobilized onto beads or similarmixable scaffolds, or immobilized onto a film or resin over which asolution of isoalpha acids is passed. The purity level of the enzyme mayvary from 30 to 90+% depending on the purification method.

Enzyme may be removed from the final product via physical filtering orcentrifugation. Enzyme may also be rendered inactive by extremetemperature or pH and remain in the final product.

As used herein ketoreductase includes commercially availableketoreductases such as KRED-P1-B05, KRED-P2-B02, KRED-P2-C02,KRED-P2-C11, KRED-P2-D11, KRED-P2-G03, KRED-P2-G09, KRED-101, KRED-119,KRED-130, KRED-NADH-110, KRED-430, KRED-431, KRED-432, KRED-433,KRED-434, KRED-435, and KRED-436 (available from Codexis, Inc., RedwoodCity, Calif.). The invention also contemplates the foregoingketoreductase which embody one or more differences in amino acidresidues, as well as ketoreductase having 99, 95, 90, 85, 80, 75 and/or70 percent homology with the foregoing ketoreductases.

The invention also includes ketoreductases purposely produced throughknown mutagenesis methods displaying variable activity on a single or amixture of isoalpha acids. Some variants are significantly improved insubstrate tolerance, temperature tolerance, solvent tolerance, and/orturnover compared to commercially available ketoreductases.

As used herein, “percentage of sequence homology,” “percent homology,”and “percent identical” refer to comparisons between polynucleotidesequences or polypeptide sequences, and are determined by comparing twooptimally aligned sequences over a comparison window, wherein theportion of the polynucleotide or polypeptide sequence in the comparisonwindow may comprise additions or deletions (i.e., gaps) as compared tothe reference sequence for optimal alignment of the two sequences. Thepercentage is calculated by determining the number of positions at whicheither the identical nucleic acid base or amino acid residue occurs inboth sequences or a nucleic acid base or amino acid residue is alignedwith a gap to yield the number of matched positions, dividing the numberof matched positions by the total number of positions in the window ofcomparison and multiplying the result by 100 to yield the percentage ofsequence identity. Determination of optimal alignment and percentsequence homology is performed using the BLAST and BLAST 2.0 algorithms(See e.g., Altschul et al., J. Mol. Biol. 215: 403-410 [1990]; andAltschul et al., Nucleic Acids Res. 3389-3402 [1977]). Software forperforming BLAST analyses is publicly available through the NationalCenter for Biotechnology Information website.

EXAMPLES

The following examples illustrate the invention without limiting itsscope.

Example 1 E. coli Expression Hosts Containing Recombinant KRED Genes

KRED-encoding genes were cloned into the expression vector pCK110900(See, FIG. 3 of US Pat. Appln. Publn. No. 2006/0195947), operativelylinked to the lac promoter under control of the lac1 repressor. Theexpression vector also contains the P15a origin of replication and achloramphenicol resistance gene. The resulting plasmids were transformedinto E. coli W3110, using standard methods known in the art. Thetransformants were isolated by subjecting the cells to chloramphenicolselection, as known in the art (See e.g., U.S. Pat. No. 8,383,346 andWO2010/144103).

Example 2 Preparation of HTP KRED-Containing Wet Cell Pellets

E. coli cells containing recombinant KRED-encoding genes from monoclonalcolonies were inoculated into 190 μl Luria-Bertani (LB) broth containing1% glucose and 30 μg/mL chloramphenicol in the wells of 96-wellshallow-well microtiter plates. The plates were sealed with O₂-permeableseals, and cultures were grown overnight at 20° C., 200 rpm, and 85%humidity. Then, 20 μl of each of the cell cultures were transferred intothe wells of 96-well deep-well plates containing 380 μL Terrific Broth(TB) and 30 μg/mL chloramphenicol (CAM). The deep-well plates weresealed with O₂-permeable seals and incubated at 30° C., 250 rpm, and 85%humidity until an OD₆₀₀ of 0.6-0.8 was reached. The cell cultures werethen induced by addition of Isopropyl β-d-1-thiogalactopyranoside (IPTG)to a final concentration of 1 mM and incubated overnight under the sameconditions as originally used. The cells were then pelleted usingcentrifugation at 4° C., 4000 rpm for 10 min. The supernatants werediscarded, and the pellets frozen at −80° C. prior to lysis.

Example 3 Preparation of HTP KRED-Containing Cell Lysates

First, the cell pellets that were produced as described in Example 2were lysed by adding 150 μL lysis buffer containing 100 mM pH 8triethanolamine*H₂SO₄ with 2 mM MgSO₄ or 100 mM pH 8 Potassium Phosphatewith 2 mM MgSO₄, 1 g/L lysozyme, and 0.5 g/L polymixin B sulfate (PMBS).Then, the cell pellets were shaken at room temperature for 2 hours on abench top shaker. The plates were centrifuged at 4000 rpm, for 15minutes at 4° C. to remove cell debris. The supernatants were then usedin biocatalytic reactions to determine their activity levels.

Example 4 Preparation of Lyophilized Lysates from Shake Flask (SF)Cultures

Shake-flask procedures can be used to generate engineered KREDpolypeptide shake-flask powders (SFP), which are useful for secondaryscreening assays and/or use in the biocatalytic processes describedherein. Shake flask powder (SFP) preparation of enzymes provides a morepurified preparation (e.g., up to 30% of total protein) of theengineered enzyme, as compared to the cell lysate used in highthroughput (HTP) assays and also allows for the use of more concentratedenzyme solutions. To start this, selected HTP cultures grown asdescribed above were plated onto LB agar plates with 1% glucose and 30μg/ml CAM, and grown overnight at 37° C. A single colony from eachculture was transferred to 6 ml of LB with 1% glucose and 30 μg/ml CAM.The cultures were grown for 18 h at 30° C. at 250 rpm, and subculturedapproximately 1:50 into 250 ml of TB containing 30 μg/ml CAM, to a finalOD₆₀₀ of 0.05. The cultures were grown for approximately 3 hours at 30°C. at 250 rpm to an OD₆₀₀ between 0.8-1.0 and induced with 1 mM IPTG.The cultures were then grown for 20 h at 30° C. at 250 rpm. The cultureswere centrifuged (4000 rpm for 20 min at 4° C.). The supernatant wasdiscarded, and the pellets were re-suspended in 35 ml of 50 mM pH 8Potassium Phosphate with 2 mM MgSO₄. The re-suspended cells werecentrifuged (4000 rpm for 20 min at 4° C.). The supernatant wasdiscarded, and the pellets were re-suspended in 6 ml of 50 mM pH 8Potassium Phosphate with 2 mM MgSO₄, and the cells were lysed using acell disruptor from Constant Systems (One Shot). The lysates werepelleted (10,000 rpm for 60 min at 4° C.), and the supernatants werefrozen and lyophilized to generate shake flask (SF) enzymes.

Example 5 Screening of Commercially Available KRED Enzyme Panel KREDScreening Assay

A set of commercially available ketoreductases were tested for theirability to reduce isoalpha acids using the commercially available “KREDScreening Kits” (Codexis Inc., Redwood City, Calif.). For a portion ofthe enzymes in this screening, the enzyme assay was carried out in a 1.5mL volume tubes, in 1000 μL total volume/tube, which included 10 g/Lenzyme powder, 2.9 or 6.9 g/L isoalpha acids substrate, and 0.8 g/L NADPin 30 vol % isopropanol (IPA) in 128 mM pH 7 sodium phosphate with 1.7mM MgSO₄. The tubes were closed and incubated at 30° C. with shaking at180 rpm for 24-48 hours. The obtained reaction mixture was filtered toremove enzyme using a 10,000 MWCO centrifugal filtration device.Isoalpha acids and dihydro-(rho)-isoalpha acids were quantified by UPLC.See, for example, the chromatogram for Codexis KRED-433 presented inFIG. 4.

For the other portion of the enzymes in this screening, the enzyme assaywas carried out in a 1.5 mL volume tubes, in 1000 μL total volume/tube,which included 10 g/L enzyme powder, 1.5 g/L isoalpha acids substrate,0.8 g/L NADP, 0.7 g/L NAD, 14.4 g/L D-glucose, and 4.3 U/mL glucosedehydrogenase in 263 mM pH 7 sodium phosphate with 1.7 mM MgSO₄. Thetubes were closed and incubated at 30° C. with shaking at 180 rpm for24-48 hours. The obtained reaction mixture was filtered to remove enzymeusing a 10,000 MWCO centrifugal filtration device. Isoalpha acids anddihydro-(rho)-isoalpha acids were quantified by UPLC.

Ketoreductase Characterization Assay

Ketoreductases that produced detectable quantities ofdihydro-(rho)-isoalpha acids were further characterized under variousreaction conditions. For this purpose, the enzyme assays were carriedout in 2.0 mL volume tubes, in 1000 μL total volume/tube, which included10-20 g/L enzyme powder, 1.5-6.0 g/L isoalpha acids substrate, 0.8 g/LNADP (optionally, 0.7 g/L NAD, 14.4 g/L D-glucose, 4.3 U/mL glucosedehydrogenase or 30 vol % Isopropanol) in 100-263 mM pH 7-9 sodiumphosphate (or alternatively, Tris HCl) with 1.7 mM MgSO₄. The tubes wereclosed and incubated at 30-40° C. with shaking at 180 rpm for 24-48hours. The obtained reaction mixtures were filtered to remove enzyme.Isoalpha acids and dihydro-(rho)-isoalpha acids were detected byUPLC-MS/MS and HPLC.

Results KRED Screening Results

Several commercially available enzymes from Codexis' “KRED ScreeningKits” are capable of reducing isoalpha acids (Table 1). The original kitwas composed of 24 ketoreductases (referred to as KREDs) that have beenselected (i.e. natural) or engineered for broad substrate range andenhanced activity by the manufacturer. An additional kit was composed of7 engineered variants based on the backbone of KRED-130.

TABLE 1 Results from Commercially Available KRED Enzyme PanelKetoreductase Enzyme Rho Detected?¹ KRED-P1-A04 − KRED-P1-A12 −KRED-P1-B02 − KRED-P1-B05 + KRED-P1-B10 − KRED-P1-B12 − KRED-P1-C01 −KRED-P1-H08 − KRED-P2-B02 + KRED-P2-C02 + KRED-P2-C11 + KRED-P2-D03 −KRED-P2-D11 + KRED-P2-D12 − KRED-P2-G03 + KRED-P2-H07 − KRED-P3-B03 −KRED-P3-G09 + KRED-P3-H12 − KRED-101 + KRED-119 + KRED-130 +KRED-NADH-101 − KRED-NADH-110 + KRED-430 + KRED-431 + KRED-432 +KRED-433 + KRED-434 + KRED-435 + KRED-436 + ¹+ = Peaks corresponding toDihydroisoalpha acids (Rho) observed via UPLC-MS after incubation withenzyme.

Ketoreductase Characterization

Enzymes were determined to reduce isoalpha acids if peaks correspondingto cis/trans-co/ad/n-dihydro-(rho)-isoalpha acid were detected via UPLCat a greater intensity than a control sample lacking enzyme.

KRED-P1-B05 (SEQ ID NO: 4) produced the most dihydro-(rho)-isoalphaacids in a 24 hour period by qualitative comparison of UPLC peak heights(See FIG. 2). KRED-P1-B05 (SEQ ID NO: 4) is derived from an enzymeencoded by a nucleotide (SEQ ID NO: 1) which encodes an amino acidsequence which is a naturally-occurring, wild-type ketoreductase fromLactobacillus kefir (SEQ ID NO: 2). Dihydro-(rho)-isoalpha acidsproduced by this ketoreductase were present at high enough concentrationto be quantified by HPLC. In 24 hour at 30° C., KRED-P1-B05 achieved ayield of 18% dihydro-(rho)-isoalpha acids. The reaction was duplicatedwith a 48 hour reaction duration, achieving a yield of 42%dihydro-(rho)-isoalpha acids. (See FIG. 3). When the reactiontemperature was increased from 30° C. to 37° C. for 48 hours, the yieldwas 33%.

KRED-P1-B05 activity was initially tested using buffer (128 mM sodiumphosphate pH 7 with 1.7 mM magnesium sulfate, 0.8 g/L mM NADP) inaddition to 30 vol % isopropanol for cofactor recycling. Multiplereaction conditions (temperature, duration, buffer composition,substrate concentration, etc.) were determined to be adequate forreduction of isoalpha acids.

Substrate Specificity

The ideal ketoreductase for biotransformation purposes shows nosubstrate specificity for the isohumulone congeners which vary based onside chain composition (conferring n-, ad-, and co-isohumulone).Additionally, the ketoreductase shows no specificity for the isohumulonecis and trans isomers which vary spatially at the C4 tertiary alcoholgroup proximal to the site of enzymatic reduction. Substrate specificityis dictated by the amino acid sequence and thus the geometry of thesubstrate binding pocket of an enzyme. Larger binding pocketsaccommodate larger substrates, as well as a greater variety ofsubstrates, compared to more restricted binding pockets.

Despite the presence of two additional ketone groups on the isoalphaacid molecule, only the desired reduction at the C4 side chain wasobserved for all characterized ketoreductases.

Example 6 Evolution and Screening of Engineered Polypeptides Derivedfrom SEQ ID NO: 4 for Improved KRED Activity

The enzyme of SEQ ID NO: 4 was selected as the parent enzyme based onthe results of screening variants for the reduction of the ene-acidsubstrate. Libraries of engineered genes were produced usingwell-established techniques (e.g., saturation mutagenesis, andrecombination of previously identified beneficial mutations). Thepolypeptides encoded by each gene were produced in HTP as described inExample 2, and the soluble lysate was generated as described in Example3.

The engineered polynucleotide of SEQ ID NO: 3 which encodes SEQ ID NO:4, exhibiting superior KRED activity, was used to generate the furtherengineered polypeptides of Table 2. These polypeptides displayedimproved formation of dihydro-(rho)-isoalpha acids from isoalpha acids,as compared to the starting polypeptide. The engineered polypeptideswere generated from the “backbone” amino acid sequence of SEQ ID NO: 4using directed evolution methods as described above together with theHTP assay and analytical methods described below in Table 2.

TABLE 2 KRED Variant Activity Relative to SEQ ID NO: 4 SEQ ID NO:Percent Conversion Fold Improvement (nt/aa) (Relative to SEQ ID NO: 4)¹5/6 ++++ 7/8 +++  9/10 +++ 11/12 +++ 13/14 ++ 15/16 ++ 17/18 ++ 19/20 ++21/22 ++ 23/24 + 25/26 + 27/28 + 29/30 + 31/32 + 33/34 + 35/36 + 37/38 +39/40 + 41/42 + 43/44 + 45/46 + 47/48 + 49/50 + 51/52 + 53/54 + 55/56 +57/58 + 59/60 + 61/62 + 63/64 + 65/66 + 67/68 + 69/70 + ¹Levels ofincreased activity were determined relative to the reference polypeptideof SEQ ID NO: 4 and defined as follows: “+” >1.0 but <2.0, “++” ≥2 but≤4, “+++” ≥4 but ≤8, “++++” ≥8

Directed evolution began with the polynucleotide set forth in SEQ ID NO:3. Engineered polypeptides were then selected as starting “backbone”gene sequences. Libraries of engineered polypeptides were generatedusing various well-known techniques (e.g., saturation mutagenesis,recombination of previously identified beneficial amino aciddifferences) and screened using HTP assay and analysis methods thatmeasured the polypeptides ability to convert the isoalpha acidssubstrates to the desired dihydro-(rho)-isoalpha acids products.

The enzyme assay was carried out in a 96-well format, in 200 μL totalvolume/well, which included 50% v/v HTP enzyme lysate, 8 g/L isoalphaacids substrate, and 0.1 g/L NADP in 40 vol % isopropanol (IPA) in 100mM pH 8 triethanolamine*H₂SO₄ with 2 mM MgSO₄. The plates were sealedand incubated at 40° C. with shaking at 600 rpm for 20-24 hours.

After 20-24 hours, 1000 μL of acetonitrile with 0.1% acetic acid wasadded. The plates were sealed and centrifuged at 4000 rpm at 4° C. for10 min. The quenched sample was further diluted 4-5× in 50:50acetonitrile:water mixture prior to HPLC analysis. The HPLC runparameters are described below in Table 3.

TABLE 3 HPLC Parameters Instrument Agilent 1100 HPLC Column 30 × 50 mm2.7 μm Waters XBridge Phenyl column Mobile Phase A: 0.1% acetic acid inwater, B: 0.1% acetic acid in acetonitrile Run 42:58 A/B for 1 minute;ramp to 10:90 A/B over parameters 1 minute Flow Rate 1.5 mL/min Run time2.0 min Com- retention pound time [min] note Peak Iso-1 0.6 mixture ofco-Iso isomers Retention Iso-2 0.7 mixture of n/ad-Iso isomers TimesIso-3 0.8 mixture of n/ad-Iso isomers Rho-1 1.0 mixture of co-Rhoisomers Rho-2 1.2 mixture of n/ad-Rho isomers Rho-3 1.4 mixture ofn/ad-Rho isomers Column 50° C. Temperature Injection 10 μL VolumeDetection 260 nm

Example 7 Evolution and Screening of Engineered Polypeptides Derivedfrom SEQ ID NO: 6 for Improved KRED Activity

Libraries of engineered genes were produced using well-establishedtechniques (e.g., saturation mutagenesis, and recombination ofpreviously identified beneficial mutations). The polypeptides encoded byeach gene were produced in HTP as described in Example 2, and thesoluble lysate was generated as described in Example 3.

The engineered polynucleotide of SEQ ID NO: 5, which encodes thepolypeptide of SEQ ID NO: 6, exhibiting superior KRED activity, was usedto generate the further engineered polypeptides of Table 4. Thesepolypeptides displayed improved formation of dihydro-(rho)-isoalpha acidfrom isoalpha acids as compared to the starting polypeptide. Theengineered polypeptides were generated from the “backbone” amino acidsequence of SEQ ID NO: 6 using directed evolution methods as describedabove together with the HTP assay and analytical methods described inTable 3.

TABLE 4 KRED Variant Activity Relative to SEQ ID NO: 6 SEQ ID NO:Percent Conversion Fold Improvement (nt/aa) (Relative to SEQ ID NO: 6)¹71/72 ++++ 73/74 +++ 75/76 +++ 77/78 +++ 79/80 +++ 81/82 ++ 83/84 ++85/86 + 87/88 + 89/90 + 91/92 + 93/94 + 95/96 + 97/98 + ¹Levels ofincreased activity were determined relative to the reference polypeptideof SEQ ID NO: 6 and defined as follows: “+” >1.0 but <2.0, “++” ≥2 but≤4, “+++” ≥4 but ≤8, “++++” ≥8

Directed evolution began with the polynucleotide set forth in SEQ ID NO:5. Engineered polypeptides were then selected as starting “backbone”gene sequences. Libraries of engineered polypeptides were generatedusing various well-known techniques (e.g., saturation mutagenesis,recombination of previously identified beneficial amino aciddifferences) and screened using HTP assay and analysis methods thatmeasured the polypeptides ability to convert the isoalpha acidsubstrates to the desired dihydro-(rho)-isoalpha acid products.

The enzyme assay was carried out in a 96-well format, in 200 μL totalvolume/well, which included 50% v/v HTP enzyme lysate, 16 or 40 g/L ofisoalpha acids substrate, and 0.1 g/L NADP in 40 vol % isopropanol (IPA)in 100 mM pH 8 triethanolamine*H2SO4 with 2 mM MgSO4. The plates weresealed and incubated at 40° C. with shaking at 600 rpm for 20-24 hours.

After 20-24 hours, 1000 μL of acetonitrile with 0.1% acetic acid wasadded. The plates were sealed and centrifuged at 4000 rpm at 4° C. for10 min. The quenched sample was further diluted 10-20× in 50:50acetonitrile:water mixture prior to HPLC analysis. The HPLC runparameters are described in Table 3.

Example 8 Evolution and Screening of Engineered Polypeptides Derivedfrom SEQ ID NO: 80 for Improved KRED Activity

Libraries of engineered genes were produced using well-establishedtechniques (e.g., saturation mutagenesis, and recombination ofpreviously identified beneficial mutations). The polypeptides encoded byeach gene were produced in HTP as described in Example 2, and thesoluble lysate was generated as described in Example 3.

The engineered polynucleotide of SEQ ID NO: 79, which encodes thepolypeptide of SEQ ID NO: 80, exhibiting superior KRED activity, wasused to generate the further engineered polypeptides of Table 5. Thesepolypeptides displayed improved formation of dihydro-(rho)-isoalphaacids from isoalpha acids as compared to the starting polypeptide. Theengineered polypeptides were generated from the “backbone” amino acidsequence of SEQ ID NO: 80 using directed evolution methods as describedabove together with the HTP assay and analytical methods described belowin Table 3.

TABLE 5 KRED Variant Activity Relative to SEQ ID NO: 80 SEQ ID NO:Percent Conversion Fold Improvement (nt/aa) (Relative to SEQ ID NO: 80)¹ 99/100 ++++ 101/102 ++++ 103/104 +++ 105/106 +++ 107/108 +++ 109/110+++ 111/112 +++ 113/114 ++ 115/116 ++ 117/118 ++ 119/120 ++ 121/122 ++123/124 ++ 125/126 ++ 127/128 ++ 129/130 + 131/132 + 133/134 + 135/136 +137/138 + 139/140 + 141/142 +

Directed evolution began with the polynucleotide set forth in SEQ ID NO:79. Engineered polypeptides were then selected as starting “backbone”gene sequences. Libraries of engineered polypeptides were generatedusing various well-known techniques (e.g., saturation mutagenesis,recombination of previously identified beneficial amino aciddifferences) and screened using HTP assay and analysis methods thatmeasured the polypeptides ability to convert the isoalpha acidsubstrates to the desired dihydro-(rho)-isoalpha acid products.

The enzyme assay was carried out in a 96-well format, in 200 μL totalvolume/well, which included 25% v/v HTP enzyme lysate, 60 or 80 g/L ofisoalpha acid substrate, and 0.02 g/L NADP in 40 vol % isopropanol (IPA)in 100 mM pH 8 potassium phosphate with 2 mM MgSO₄. The plates weresealed and incubated at 45° C. with shaking at 600 rpm for 20-24 hours.

After 20-24 hours, 1000 μL of acetonitrile with 0.1% acetic acid wasadded. The plates were sealed and centrifuged at 4000 rpm at 4° C. for10 min. The quenched sample was further diluted 20-40× in 50:50acetonitrile:water mixture prior to HPLC analysis. The HPLC runparameters are described in Table 3.

Example 9 Evolution and Screening of Engineered Polypeptides Derivedfrom SEQ ID NO: 80 for Improved KRED Activity at High SubstrateConcentration

Libraries of engineered genes were produced using well-establishedtechniques (e.g., saturation mutagenesis, and recombination ofpreviously identified beneficial mutations). The polypeptides encoded byeach gene were produced in HTP as described in Example 2, and thesoluble lysate was generated as described in Example 3.

The engineered polynucleotide of SEQ ID NO: 79, which encodes thepolypeptide of SEQ ID NO: 80, exhibiting superior KRED activity, wasused to generate the further engineered polypeptides of Table 6. Thesepolypeptides displayed improved formation of dihydro-(rho)-isoalphaacids from isoalpha acids as compared to the starting polypeptide. Theengineered polypeptides were generated from the “backbone” amino acidsequence of SEQ ID NO: 80 using directed evolution methods as describedabove and are described below in Table 3.

TABLE 6 KRED Variant Activity Relative to SEQ ID NO: 80 SEQ ID NO:Percent Conversion Fold Improvement (nt/aa) (Relative to SEQ ID NO: 80)¹143/144 ++++ 145/146 ++++ 147/148 ++++ 149/150 ++++  99/100 ++++ 151/152+++ 153/154 +++ 155/156 +++ 103/104 ++ 157/158 ++ 159/160 ++ 139/140 +161/162 +

Directed evolution began with the polynucleotide set forth in SEQ ID NO:79. Engineered polypeptides were then selected as starting “backbone”gene sequences. Libraries of engineered polypeptides were generatedusing various well-known techniques (e.g., saturation mutagenesis,recombination of previously identified beneficial amino aciddifferences) and screened using HTP assay and analysis methods thatmeasured the polypeptides ability to convert the isoalpha acidsubstrates to the desired dihydro-(rho)-isoalpha acid products.

The enzyme assay was carried out in a 96-well format, in 200 μL totalvolume/well, which included 10-20% v/v HTP enzyme lysate, 80 or 160 g/Lof isoalpha acid substrate, and 0.02 g/L NADP in 40 vol % isopropanol(IPA) in 100 mM pH 8 potassium phosphate with 2 mM MgSO₄. The plateswere sealed and incubated at 45° C. with shaking at 600 rpm for 20-24hours.

After 20-24 hours, 1000 μL of acetonitrile with 0.1% acetic acid wasadded. The plates were sealed and centrifuged at 4000 rpm at 4° C. for10 min. The quenched sample was further diluted 20-40× in 50:50acetonitrile:water mixture prior to HPLC analysis. The HPLC runparameters are described in Table 3.

Example 10 Evolution and Screening of Engineered Polypeptides Derivedfrom SEQ ID NO: 80, 104, 100, 136, 116, 132, 162, 150, 152, 144 and 146for Improved KRED Activity at High Substrate and Low NADP Concentration

A 200 g/L enzyme stock solution was prepared by dissolving 100 mg ofenzyme powder in 500 μL of 100 mM pH 8 potassium phosphate buffer with 2mM MgSO4 and 0.1 g/L of NADP. To a well in a 96 deep-well plate wasadded 40 μL of the enzyme/NADP stock solution, 80 μL of isopropanol, and80 μL of 40 wt % aqueous solution of isoalpha acid. The final reactioncomposition was 40 g/L of enzyme, 160 g/L isoalpha acid, and 0.02 g/LNADP in 40% IPA. The plate was sealed and incubated 40° C. for 24 h andthen quenched and analyzed by HPLC-UV. The data are shown in Table 7 andFIG. 5.

TABLE 7 KRED Activity at High Substrate and Low NADPH Concentration SEQID NO: % Conversion (nt/aa) 40 g/L 20 g/L 10 g/L 5 g/L 2.5 g/L 1.25 g/L79/80 4.2 1.9 0.9 0.5 0.1 0.0 103/104 28.2 16.5 8.7 5.2 2.2 1.2  99/10023.1 11.2 6.1 3.3 1.3 0.6 135/136 23.6 7.5 2.4 1.2 0.6 0.0 115/116 8.53.2 1.2 0.7 0.2 0.0 131/132 5.3 2.2 0.8 0.4 0.1 0.0 161/162 29.1 14.45.6 2.1 0.7 0.3 149/150 29.0 14.9 6.0 2.4 1.0 0.2 151/152 30.6 17.9 7.43.6 2.0 1.2 143/144 29.1 14.4 5.8 2.4 1.2 0.4 145/146 24.3 12.3 4.7 1.90.8 0.1 157/158 3.0 1.1 0.4 0.0 0.0 0.0

Example 11 Enzyme Treatment of Acidified Hop Derived Isoalpha Acids withCofactor Recycling by Isopropanol Oxidation

Isoalpha acids are treated in a manner described in Example 10, wherethe source of isoalpha acids is a highly concentrated material (68.9%isoalpha acids) having a pH<7.

Example 12 Enzyme Treatment of Hop Derived Isoalpha Acids with CofactorRecycling by Glucose Dehydrogenase

Isoalpha acids are treated in a manner described in Example 10, with theexception that isopropanol is replaced with 4.3 U/mL GlucoseDehydrogenase, 0.7 g/L mM NAD, and 14.4 g/L D-glucose.

Example 13 Enzyme Treatment of Hop Derived Isoalpha Acids withoutCofactor Recycling

Isoalpha acids are treated in a manner described in Example 10, with theexception that isopropanol is replaced with an equimolar amount of NADPHas substrate.

Example 14 Enzyme Treatment of Hop Derived Isoalpha Acids with CofactorRecycling by Ethanol Oxidation

Isoalpha acids are treated in a manner described in Example 10, with theexception that isopropanol is replaced with ethanol.

Example 15 Enzyme Treatment of Hop Derived Isoalpha Acids withImmobilized Ketoreductase Via SiO₂

A ketoreductase is adsorbed on SiO₂ and crosslinked with glutaraldehydeto yield an immobilized ketoreductase material. Isoalpha acids aretreated with the immobilized ketoreductase in a manner described inExample 10. The obtained reaction mixture is centrifuged at 10,000 g toremove immobilized enzyme.

Example 16 Enzyme Treatment of Hop Derived Isoalpha Acids withImmobilized Ketoreductase Via DEAE-Cellulose

A ketoreductase is crosslinked with glutaraldehyde and adsorbed ontoDEAE-cellulose to yield an immobilized ketoreductase material. Isoalphaacids are treated with the immobilized ketoreductase in a mannerdescribed in Example 10. The obtained reaction mixture is centrifuged at10,000 g to remove immobilized enzyme.

Example 17 Enzyme Treatment of Hop Derived Isoalpha Acids withImmobilized Ketoreductase Via PEI-Treated Alumina

A ketoreductase is crosslinked with glutaraldehyde and adsorbed ontopolyethylimine (PEI)-treated alumina to yield an immobilizedketoreductase material. Isoalpha acids are treated with the immobilizedketoreductase in a manner described in Example 10. The obtained reactionmixture is centrifuged at 10,000 g to remove immobilized enzyme.

Example 18 Enzyme Treatment of Hop Derived Isoalpha Acids with NADHCofactor Recycling

Enzyme treatment where the NADPH cofactor is substituted with NADH.Isoalpha acids are treated in a manner described in Example 10 but theNADP is replaced with NAD.

Example 19 Enzyme Treatment of Hop Derived Isoalpha Acids Followed byExtraction

Enzyme treatment followed by extraction to increase final concentrationof dihydro-(rho)-isoalpha acids is performed. Isoalpha acids are treatedin a manner described in Example 10. The obtained reaction mixture isfiltered to remove enzyme and extracted with food-grade solvent toachieve a desired concentration of dihydro-(rho)-isoalpha acids.

Example 20 Enzyme Treatment of Hop Derived Isoalpha Acids Followed byThermal Inactivation

Isoalpha acids are treated in a manner described in Example 10. Thereaction is incubated at 30° C. with orbital shaking at 180 rpm for 24hours. The obtained reaction mixture is heated at 80-100° C. for 10-30minutes to inactivate enzyme.

Example 21 Enzyme Treatment of Hop Derived Isoalpha Acids Followed byChemical Inactivation

Isoalpha acids are treated in a manner described in Example 10. Thereaction is incubated at 30° C. with orbital shaking at 180 rpm for 24hours. Food-grade ethanol is added to a final concentration of >50% toinactivate enzyme.

Example 22 Enzyme Treatment of Hop Derived Isoalpha Acids withImmobilized Ketoreductase Recycling

A ketoreductase is crosslinked with glutaraldehyde and adsorbed ontoDEAE-cellulose to yield an immobilized ketoreductase material. Isoalphaacids are then treated with the immobilized ketoreductase in a mannerdescribed in Example 10. The obtained reaction mixture is centrifuged at10,000 g to separate immobilized ketoreductase from the reactionsolution. Immobilized ketoreductase is recovered, washed with water oraqueous buffer, and re-used in a new reaction mixture.

CONCLUSIONS

162 ketoreductases have been characterized as transforming isoalphaacids into dihydro-(rho)-isoalpha acids. The ketoreductasescharacterized in this study possess an enzymatic activity that has notbeen described previously. The ketoreductases characterized in thisstudy all reduce a ketone group into an alcohol and are thusketoreductases. These results demonstrate that a ketoreductasebiocatalyst may be employed to convert isoalpha acids todihydro-(rho)-isoalpha acids in a novel biotransformation process. Thepresent invention is intended to replace current processes utilizingsodium borohydride.

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described herein will become apparent tothose skilled in the art from the foregoing description. Suchmodifications are intended to fall within the scope of the appendedclaims.

All patents, applications, publications, test methods, literature, andother materials cited herein are hereby incorporated by reference.

CITED REFERENCES

-   1. Sodium Borohydride; MSDS No. S9125; Sigma-Aldrich Co.: Saint    Louis, Mo. Nov. 1, 2015. (accessed 06/08/17).-   2. Robinson, P. K., Enzymes: principles and biotechnological    applications. Essays Biochem 2015, 59, 1-41.-   3. Hult, K.; Berglund, P., Enzyme promiscuity: mechanism and    applications. Trends Biotechnol. 2007, 25 (5), 231-238.-   4. Nobeli, I.; Favia, A. D.; Thornton, J. M., Protein promiscuity    and its implications for biotechnology. Nat. Biotechnol. 2009, 27    (2), 157-167.-   5. Pozen, M., Enzymes in Brewing. Ind. Eng. Chem, 1934, 26 (11),    1127-1133.-   6. Praet, T.; Opstaele, F.; Jaskula-Goiris, B.; Aerts, G.; De    Cooman, L., Biotransformations of hop-derived aroma compounds by    Saccharomyces cerevisiae upon fermentation. Cerevisia, 2012, 36,    125-132.-   7. Wallerstein, L. (1947) Bentonite and Proteolytic Enzyme Treatment    of Beer, U.S. Pat. No. 2,433,411.-   8. Ghionno, L.; Marconi, O.; Sileoni, V.; De Francesco, G.;    Perretti, G., Brewing with prolyl endopeptidase from Aspergillus    niger the impact of enzymatic treatment on gluten levels, quality    attributes, and sensory profile. Int. J. Food Sci. Technol, 2017, 52    (6), 1367-1374.-   9. Gros, J.; Tran, T. T. H.; Collin, S., Enzymatic release of    odourant polyfunctional thiols from cysteine conjugates in hop. J.    Inst. Brew. 2013, 119 (4), 221-227.

1. A process for the preparation of dihydro-(rho)-isoalpha acids,comprising treating isoalpha acids with a ketoreductase enzyme or amicroorganism expressing a gene that encodes the ketoreductase.
 2. Theprocess according to claim 1, wherein the process is carried out in anaqueous system.
 3. The process according to claim 2, wherein the processis carried out under mild temperature and pH conditions.
 4. The processaccording to claim 1, comprising addition of the ketoreductase enzymeand NADPH or NADP to a mixture of isoalpha acids followed by incubation.5. The process according to claim 1, comprising adding the ketoreductaseenzyme and NADPH or NADP to a mixture of isoalpha acids in the presenceof isopropanol for cofactor recycling, followed by incubation.
 6. Theprocess according to claim 1, wherein the concentration of isoalphaacids, i.e. the substrate, is maximized to increase the volumetricproductivity of the bioconversion.
 7. The process according to claim 1,wherein the concentration of the cofactor NADPH or NADP in the mixtureis minimized to improve the economics of the bioconversion.
 8. Theprocess according to claim 1, comprising adding the ketoreductase enzymeand NADPH or NADP to a mixture of isoalpha acids in the presence ofanother enzyme for cofactor recycling, followed by incubation.
 9. Theprocess according to claim 1, comprising adding a whole cellbiocatalyst, wherein the whole cell biocatalyst is an immobilizedmicroorganism expressing the gene which encodes a ketoreductase, to amixture of isoalpha acids followed by incubation.
 10. The processaccording to claim 1, comprising treating isoalpha acids with a growingmicroorganism expressing a gene which encodes the ketoreductase.
 11. Theprocess according to claim 1, comprising adding the ketoreductaseenzyme, wherein the ketoreductase is thermostable, to an extract ofisoalpha acids wherein heat is applied, and the mixture is incubated.12. The process according to claim 1, wherein the ketoreductasespecifically reduces cis-isohumulone, cis-isocohumulone, andcis-isoadhumulone.
 13. The process according to claim 1, wherein theketoreductase specifically reduces trans-isohumulone,trans-isocohumulone, and trans-isoadhumulone.
 14. The process accordingto claim 1, comprising adding a mixture of 2 or more ketoreductaseenzymes to reduce a mixture of cis- and trans-isoalpha acids, to theirrespective dihydroisoalpha acids.
 15. The process according to claim 14,wherein the mixture of 2 or more ketoreductase enzymes produces a uniquemixture of dihydroisoalpha acids that is distinct from that produced bychemical reducing agents, such as sodium borohydride.
 16. The processaccording to claim 1, wherein the ketoreductase enzyme is selected fromthe group consisting of KRED-P1-B05, KRED-P2-B02, KRED-P2-C02,KRED-P2-C11, KRED-P2-D11, KRED-P2-G03, KRED-P2-G09, KRED-101, KRED-119,KRED-130, KRED-NADH-110, KRED-430, KRED-431, KRED-432, KRED-433,KRED-434, KRED-435, and KRED-436.
 17. The process according to claim 16,wherein the ketoreductase enzyme or microorganism expressing a genewhich encodes the ketoreductase can optionally have one or moredifferences at amino acid residues as compared to the ketoreductaseenzyme selected from the group consisting of KRED-P1-B05, KRED-P2-B02,KRED-P2-C02, KRED-P2-C11, KRED-P2-D11, KRED-P2-G03, KRED-P2-G09,KRED-101, KRED-119, KRED-130, KRED-NADH-110, KRED-430, KRED-431,KRED-432, KRED-433, KRED-434, KRED-435, and KRED-436.
 18. The processaccording to claim 17, wherein the ketoreductase is 99, 95, 90, 85, 80,75 or 70 percent homologous to the ketoreductase enzyme selected fromthe group consisting of KRED-P1-B05, KRED-P2-B02, KRED-P2-C02,KRED-P2-C11, KRED-P2-D11, KRED-P2-G03, KRED-P2-G09, KRED-101, KRED-119,KRED-130, KRED-NADH-110, KRED-430, KRED-431, KRED-432, KRED-433,KRED-434, KRED-435, and KRED-436.
 19. The process according to claim 1,wherein the ketoreductase enzyme comprises an amino acid sequenceselected from the group consisting of SEQ ID NO: 4, SEQ ID NO: 6, SEQ IDNO: 80, SEQ ID NO: 104, SEQ ID NO: 100, SEQ ID NO: 136, SEQ ID NO: 116,SEQ ID NO: 132, SEQ ID NO: 162, SEQ ID NO: 150, SEQ ID NO: 152, SEQ IDNO: 144, SEQ ID NO: 146 and SEQ ID NO:
 158. 20. The process according toclaim 19, wherein the ketoreductase enzyme or microorganism expressing agene which encodes the ketoreductase can optionally have one or moredifferences at amino acid residues as compared to the ketoreductaseenzyme selected from the group consisting of SEQ ID NO: 4, SEQ ID NO: 6,SEQ ID NO: 80, SEQ ID NO: 104, SEQ ID NO: 100, SEQ ID NO: 136, SEQ IDNO: 116, SEQ ID NO: 132, SEQ ID NO: 162, SEQ ID NO: 150, SEQ ID NO: 152,SEQ ID NO: 144, SEQ ID NO: 146 and SEQ ID NO:
 158. 21. The processaccording to claim 20, wherein the ketoreductase is 99, 95, 90, 85, 80,75 or 70 percent homologous to the ketoreductase enzyme selected fromthe group consisting of SEQ ID NO: 4, SEQ ID NO: 6, SEQ ID NO: 80, SEQID NO: 104, SEQ ID NO: 100, SEQ ID NO: 136, SEQ ID NO: 116, SEQ ID NO:132, SEQ ID NO: 162, SEQ ID NO: 150, SEQ ID NO: 152, SEQ ID NO: 144, SEQID NO: 146 and SEQ ID NO: 158.